A network engineer configures an IPv4 static route on a Cisco router using a next-hop IP address: ip route 192.168.50.0 255.255.255.0 10.0.12.2. When the router receives an inbound packet destined for host 192.168.50.25, in what order does the Cisco IOS routing engine process the packet to determine the forwarding path? Arrange the operational steps in the correct chronological sequence from first to last.
- 1The router receives an IPv4 packet destined for 192.168.50.25 on an inbound interface.
- 2The routing engine evaluates the routing table and finds the longest prefix match for 192.168.50.0/24.
- 3The router extracts the next-hop IPv4 address (10.0.12.2) associated with the static route.
- 4The router performs a recursive lookup in the routing table for 10.0.12.2 to identify the directly connected exit interface.
- 5The router encapsulates the IPv4 packet into a Layer 2 frame and forwards it out the resolved exit interface toward 10.0.12.2.
Answer
The correct sequence begins with the packet arrival, followed by performing the initial longest prefix match lookup in the routing table, identifying the next-hop IP address, executing a recursive lookup for that next-hop IP to determine the egress interface, and finally encapsulating and forwarding the packet out the resolved exit interface.
When a static route specifies a next-hop IPv4 address rather than a directly attached exit interface, Cisco IOS must complete a two-step lookup process. First, the router matches the destination IP to the static route entry. Second, it performs a recursive lookup on the next-hop IP address to identify the egress interface. Finally, ARP resolution completes Layer 2 encapsulation, and the frame is transmitted.
Step-by-Step Solution
Key Concept
Recursive Routing Table Lookup for IPv4 Static Routes